The present application claims priority to German Patent Application 10017259.8, filed Apr. 6, 2000.
This application claims priority to German Application No. 10017259.8, filed Apr. 6, 2000.
The invention relates to a device for feeding flat objects that overlap in slats, particularly metal sheets, to at least a front edge stopper of a processing machine, particularly a tin printing or a tin-plate varnishing machine, with a first conveyor on which the objects lie. In a known device, the speed of the entire feed belt system is reduced in cycles to slow down the objects arranged in slats. As a result, all the sheets that overlap in slats slow down simultaneously, in the course of which the frontmost sheet is placed against the front edge stopper. From there, the sheet is delivered in a position-determined manner by means of another transport system. The remaining panels are again cyclically accelerated until the frontmost panel has reached a certain position, at which point the slowdown is again carried out. The disadvantage of this system is that very large masses must be accelerated and slowed down, so that the accuracy of the position of the frontmost panel in the target braking area greatly diverges on account of belt elasticity and other parameters that exert influence. There is therefore no certain, reproducible front edge equipment of the sheet metals.
Furthermore, devices with delaying elements are known, with which a panel delay is effected through friction. The disadvantage here is the poor accuracy due to the slippage action that is hard to reproduce, which, in the target braking area, in the process of transferring to the front edge stopper, may cause too great a residual velocity when it stops (damage problem) or too much of a delay (no sufficient arrangement of the front edge of the sheet). Furthermore, it is disadvantageous that, in the conveyor, during the breaking process, the holding surface is reduced when the next metal sheet goes under. In an unfavorable case, the holding surface is reduced to zero, so that an undefined slippage occurs in the last brake phase.
The problem that the invention seeks to solve is to create a device for feeding flat objects that overlap in slats, of the type mentioned at the start, which allows a precise, reproducible arrangement of the particular front edge of the metal sheets at the front edge stopper. Moreover, a high cycle count can be realized.
This task is solved according to the invention by having the first conveyor exhibit a constant speed or a speed that changes in cycles, and a second conveyor arranged between the first conveyor and the front edge stopper, with the said second conveyor being designed as a continuously rotating run and which takes over each frontmost object from the first conveyor at a speed that matches that of the first conveyor, and slows it down to a lesser speed, particularly almost to a standstill, and in this delayed state, feeds it to the front edge stopper through subsequent sliding of the object on a base or delivery to a device, in which the device leads the object to rest on the front edge stopper, or that the run slows down the object until it comes to a standstill, to the extent that it is led up to the front edge stopper. This method results in a precise sheet alignment without damage to the corners. The objects lying in slats on the first conveyor are consequently continuously transported at constant speed. A slat transport with constant speed thus takes place. Alternatively, a speed that changes in cycles can also be designed. A speed that changes in cycles means high speed, low speed, high speed, low speed, etc., in which the speed ratio preferably lies in the range of 4:1 to 2:1, and in particular, 3:1. The frontmost metal sheet in the slatxe2x80x94as seen from the transport directionxe2x80x94is slowed down by mean of the second mean of conveyance, to the extent that it bumps into the front edge stopper at a low residual speed or that it is delivered with the low residual speed to the device, which leads it to the front end stopper. Alternatively, the slowdown can also take place through the second conveyor in such a way that the metal sheet is led from the second conveyor up to the front edge stopper where it comes to a standstill. While the frontmost sheet is decelerated, the slatted arrangement of the remaining sheets is constantly moved further by means of the first conveyor. It is also alternatively conceivable for the lamellar flow of the first conveyor to be transported in cycles. This means making a change of speed in cycles: high speed, low speed, etc. If the frontmost sheet is precisely aligned, it is taken over by a processing mechanism in a precisely aligned position. During the mentioned aligning process, the second conveyor again accelerates to a speed that corresponds to that of the first conveyor so that afterwards, the current frontmost metal sheet of the slat arrangement is taken over by the second conveyor and, as previously described, is slowed down and precisely aligned to the front edge stopper. Each frontmost sheet preferably lies on the second conveyor, and during the slowdown, no relative movement takes place between the second conveyor and the metal sheet, thereby providing an exact reproducibility. During the slowdown, no sliding movement develops in the main phase between the second conveyor and the metal sheet. The metal sheet is precisely slowed down with the second conveyor (side belt), corresponding to an established law of motion which occurs in the same placexe2x80x94machine anglexe2x80x94for each cycle. The following preferably provided holding action through vacuum, which is defined in greater detail, is designed in such a way that the course of the curve of the slowdown is independent of the weight of the sheet and of the surface condition of the metal sheet. The movement of the second conveyor and the metal sheet is synchronous in the slowing down phase, without relative movement. Only shortly before the arrival at the front edge stopper, especially at the front marks, is this frictional connection (by switching off the vacuum) neutralized so that the second conveyor still pushes the metal sheet, but only with a very slight force arising from the existing friction without vacuum between the run and the metal sheet. The scaling is done during the slowing-down process of the frontmost sheet in such a way that the overlapping zone with the subsequent sheet increases. Appropriately adopting the speed of the two conveyors while taking into account the sizes of the respective objects to be fed allows for a high processing number per time unit. The objects lie on the first and the second conveyor, i.e., the objects are above the conveyors; there is therefore no overhead transport in which the objects are held on the underside of the conveyors. This is important, among other things, because the arrangement of the objects in slats is in such a way that the frontmost sheet is grasped from underneath by the subsequent one, etc., so that the sheets are solely accessible from below only in the non-overlapped area.
As mentioned, a slowdown up to a relatively low speed follows according to the invention. Once the object has accepted this low speed, it slides a little bit over the base, and in this manner, reaches the front edge stopper and is aligned there. Alternatively, it is also possible for the objectxe2x80x94after the slowdownxe2x80x94to be taken over by another device that grasps the object (through a gripper device, suction device, and/or magnetic device) and leads it precisely up to the front edge stopper so that the alignment takes place there. Alternatively, it is also possible for the second conveyor to decelerate the object until it comes to a standstill, in which the slowdown occurs in such a way that, when the object is at a standstill, or shortly before it comes to a standstill, it bumps into the front edge stopper, causing it become aligned.
A further embodiment of the invention provides for a first retaining device to be allocated to the first conveyor. A second retaining device can preferably be allocated to the second conveyor. The first and/or the second holding device can preferably be designed as a suction device and/or as a magnetic device. The suction device is designed in such a way that the objects, particularly the metal sheets, are held against the surface of the conveyor through a suction effect, thereby definitely avoiding a relative movement between the corresponding conveyor and the objects. In particular, because of the holding action, the braking process can be carried out without the metal sheet slipping on the conveyor, thereby achieving a high precision at a high number of cycles. Insofar as the objects are ferromagnetic components, for instance, steel sheets, a magnetic device can also be used as a holding device, with said magnetic device being found underneath the conveyor, and by this method, preventing a relative dislocation between the metal sheet and conveyors. The metal sheets consequently move precisely with the speed which is specified by the corresponding conveyor.
In particular, the first conveyor can be provided as a continuously running conveyor. The first and second conveyors are consequently runs which preferably consist of several belts that lie parallel side by side, on which the metal sheets lie, with the holding device arranged underneath the top run, with the metal sheet or metal sheets holding the said holding device in place on the belts.
Furthermore, it is advantageous when the second holding devicexe2x80x94as seen from the transport directionxe2x80x94extends only over a section of the second conveyor. This section is sufficient for a positioning and keeps the positioning zone relatively small so that only correspondingly small quantities of energy are to be applied for the holding action.
Furthermore, it is advantageous when the second holding device is essentially on the power-side half of the second conveyor.
It is particularly preferred when the holding action of the second holding device can be switched on and off. In the case of a vacuum suction device, the vacuum source can be switched on and off or there is a pneumatically operative on-off valve in the system, with which the suction effect can be switched on and off. The suction effect is activated as soon as the frontmost metal sheet is taken over by the second conveyor; it is deactivated or greatly reduced immediately before the front edge of the decelerated metal sheet bumps against the front edge stopper. If there is a magnetic device for deploying the holding action, an electromagnetic device is preferably used so that the retention force can be activated or deactivated by switching on and off electronically.
The holding action of the first holding device preferably acts continuously, meaning that it is not switched on. Exception: it is switched on for the last sheet of the lamellar flow.
In particular, it can be provided for the first and/or the second holding device to be made of at least one suction box underneath the first and/or the second conveyor. The suction box is preferably connected to a vacuum source through an on-off valve. In order for the suction to have an effect on the sheets through the first and/or second conveyor, the first and/or second conveyor is designed to be air-permeable.
The invention furthermore relates to a method for feeding flat objects that overlap in slats, particularly metal sheets, to at least a front edge stopper of a processing machine, particularly a tin printing machine or a tin-plate varnishing machine, with a first feeding zone, in which the objects arranged in slats are transported at the first constant speed, and with a second feeding zone following the first feeding zone, in which each frontmost object is taken at the first speed and then slowed down to the second speed, so that it is led with the second speed to at least a front edge stopper or nears the front edge stopper at this speed.
The second speed is much less than the first speed; it preferably exhibits a very small value, or the procedure is such that the sheet is decelerated to zero, and when it comes to a standstill, the front edge of the sheet bumps against the front edge stopper.
At a nominal speed corresponding to about 9,000 to 10,000 sheets per hour, the first speed can preferably be about 1 m/s. The second speed can exhibit a value of about 0.2 or 0.1 m/s, for example. In particular, the second speed can be set at 0.25 to 0.1 times the first speed.